Heat Sink Comprising a Tube Through Which Cooling Medium Flows

ABSTRACT

There is described a heat sink having at least one tube through which cooling medium flows and which is surrounded by a heat-conducting material, wherein the tube wall of the at least one tube is corrugated in the direction of flow. The corrugated embodiment has the advantage that the transition from laminar to turbulent flow relative to a straight-walled tube is effected at a lower flow velocity and the heat transfer area is greater at the same tube length.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2006/069241, filed Dec. 4, 2006 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2006 008 033.5 DE filed Feb. 21, 2006, both of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a heat sink comprising at least one tube through which cooling medium flows and which is surrounded by a heat-conducting material.

BACKGROUND OF INVENTION

Heat sinks of said kind are used for example for cooling heat-generating components for whose operation an increase in the temperature of the ambient air is not desirable. Examples of such components are snubber resistors, power semiconductors or electrolytic capacitors in power electronics. In such cases the heat sink typically serves as a mount on which the electronic components are placed. The components are mounted onto the heat sink surface-to-surface with good thermal contact such that a transfer of heat takes place from the components onto the heat sink. At the same time this leads to the requirement for the heat to be dissipated as directly as possible to the cooling medium. If that is the case, the components exhibit very good thermal resistance and only a slight heating of the respective component environment takes place in the heat sink.

In the heat sink, heat is released to the cooling medium flowing in tubes. In such an arrangement a closed circuit is usually provided in which the cooling medium is circulated by means of a pump and cooled down by way of a heat exchanger. At the same time the aim is to keep the amount of cooling medium small in order to ensure a maximum ratio of cooling performance to device volume.

According to the prior art, embodiment variants are known in which welded high-grade steel tubes are cast in aluminum, as manufactured for example by the company Entwicklung and Fertigung Volker Eβbach, D-09600 Berthelsdorf, Germany (www.efe-essbach.de).

Effort is directed at achieving good heat transfer between heat sink and cooling medium in order to optimize cooling performance. According to the prior art turbulating elements are for that reason arranged inside the tubes in order to ensure a turbulent flow. A laminar flow is disadvantageous due to the low heat transfer coefficient.

Turbulating elements of the aforesaid kind often result in the formation inside the tubes of zones within which small amounts of cooling medium circulate or within which low flow velocities arise. This leads over time to the accumulation of waste products and residues which are precipitated from the cooling medium and adhere to the tube inner wall and the turbulating elements. The consequence of this is deterioration in heat transfer efficiency together with an increase in flow resistance which may ultimately lead to a complete blockage of the tube.

Without turbulating elements the flow velocity must be chosen high enough to ensure that a transition from laminar to turbulent flow takes place. Due to the necessary increase in the pump delivery rate this, however, leads to a drop in the overall efficiency of the cooling system and an undesirable increase in noise emission results.

SUMMARY OF INVENTION

An object underlying the present invention is to specify an improvement over the prior art for a heat sink of the type cited in the introduction.

This object is achieved according to the invention by means of a heat sink comprising at least one tube through which cooling medium flows and which is surrounded by a heat-conducting material, wherein the tube wall of the at least one tube is corrugated in the flow direction. The corrugated embodiment has the advantage that the transition from laminar to turbulent flow takes place at a lower flow velocity compared to a straight-walled tube. Turbulating elements are then no longer necessary. Furthermore the heat transfer area is greater for the same tube length compared to a straight-walled tube, as a result of which more heat is dissipated to the cooling medium.

In an advantageous embodiment of the invention it is provided that the at least one tube is embodied as a corrugated tube with parallel corrugations. Corrugated tubes of said kind are available in different materials at affordable cost. Furthermore the parallel corrugation has the advantage that a tube can easily be bent.

A further advantageous embodiment is provided if the at least one tube is embodied as a spiral tube with spiral corrugations. A tube of said kind combines the advantages of a corrugated tube with a simple means of connecting to connector fittings which have suitable internal threads and are screwed onto the ends of the spiral tube without additional preparatory work. Furthermore a better purging effect for evacuating possible cooling medium waste products is achieved in a spiral tube.

It is also advantageous if the at least one tube is manufactured from corrosion-resistant high-grade steel or copper. With high-grade steel, a long useful life of the heat sink is assured even if the cooling medium contains corrosion-promoting substances. When a cooling medium whose corrosive effect is known to be minor is employed, the use of copper is also advantageous, since its thermal conductivity is superior to high-grade steel.

It is favorable therein to provide aluminum or copper or brass or zinc as the surrounding material. These materials are well suited to casting and possess high thermal conductivity, with the result that the waste heat of the components mounted on the heat sink is dissipated directly to the cooling medium.

Another favorable embodiment variant of the invention provides that the at least one tube is formed from the heat-conducting material as a tubular cavity. In this case no separate tube is used, but instead, during a casting process, a casting core having the shape of the corrugated tube inner wall is placed in a casting mold. A cavity having the shape of the casting core is then embodied in the cast body made of heat-conducting material. A further possibility consists in embodying the heat sink in two parts with a mold seam defined by the central axis of the tube. Chip-removing machining methods are then used to produce the tubular cavity in such a way that a corrugated channel is hollowed out in each half of the heat sink. When the heat sink is assembled, these two channels form the tubular cavity.

It is also of advantage if the heat sink has an essentially plate-shaped geometry. The heat sink is then easy to manufacture and has a flat mounting surface for affixing heat-dissipating components.

It is favorable for the arrangement of the at least one tube if said tube is arranged in a meander shape. The tube then forms a plurality of cooling coils within the heat sink, thereby producing a more effective dissipation of heat to the cooling medium. Furthermore, sufficient space for mounting holes remains between the cooling coils.

Another favorable arrangement is given if the at least one tube is arranged in a spiral shape. In such an arrangement the tube is embodied e.g. in the center of the spiral with a semicircular arc, such that two tube sections running in parallel are brought out in a spiral shape and provided with connector fittings at the edge of the heat sink. As in the case of the meander-shaped arrangement, this provides a sufficient tube length within the heat sink for good heat dissipation to the cooling medium.

It is also favorable if a water/antifreeze mixture is provided as the cooling medium. A mixture of said kind is not only readily available but is also suitable for a frostproof application of the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below as an exemplary embodiment with reference to the accompanying figures, which show in schematic form:

FIG. 1: a front view and side view of a heat sink

FIG. 2: a longitudinal cross-section of a corrugated tube

FIG. 3: a longitudinal cross-section of a spiral tube

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows an exemplary embodiment of a heat sink comprising a tube 2 arranged in a meander shape, wherein the tube wall is corrugated in the flow direction. In this arrangement the tube has connector fittings 3, 4 at its ends, with cooling medium that has been cooled being pumped into the heat sink by way of a first connector fitting 3. Within the heat sink the tube 2 forms a plurality of cooling coils with semicircles being arranged between straight tube sections such that the straight successive tube sections run parallel to one another. The alignment of the tube sections running parallel to one another can be changed here within the heat sink, resulting in an adjustment to the position and heat dissipation of the components arranged on the heat sink. Components exhibiting a higher heat dissipation are therein arranged directly over one or more tube sections, whereas components exhibiting lower heat dissipation can also be placed in zones between two tube sections.

When flowing through the tube 2 arranged within the heat sink, the cooling medium absorbs heat and flows out of the heat sink by way of a second connector fitting 4, usually via a pump to a heat exchanger by means of which the cooling medium is cooled down.

The tube 2 is embodied by way of example as a corrugated tube made of corrosion-resistant high-grade steel. It is also possible to equip a heat sink with a plurality of tubes 2 and in this way provide a plurality of cooling circuits. In this case each cooling circuit can have its own particular temperature level and its own particular flow velocity, thereby ensuring an optimal matching to the cooling requirements of the components mounted on the heat sink.

The tube 2 is meander-shaped in one plane and cast in a heat-conducting material (1), aluminum for example. Thus, only the ends of the tube 2 with the connector fittings 4, 5 project from the heat-conducting material (1).

Drilled holes 5 are provided in the zones between the parallel tube sections and serve as mounting holes for installing components. The heat sink itself, however, can also be mounted on an appropriate support by means of the drilled holes 5.

When the components are mounted on the heat sink, care should be taken to ensure good heat transfer from the components to the heat sink. Where appropriate a heat-conducting substance should be provided in the gap between a component and the heat sink.

In order to determine the optimal cooling conditions it makes sense to carry out empirical tests with different tube arrangements, wherein the heat sink is initially uniformly heated in a test setup and then cooled down through circulation of a cooling medium. During the cooling-down process the change in temperature is measured as a function of time and the position on the heat sink surface. The placement of the individual components on the heat sink is subsequently carried out on the basis of these measurement results.

In corrugated or spiral tubes through which cooling medium flows, the pressure loss per tube length unit as a function of the volume flow rate follows a parabolic profile, i.e. the pressure loss per tube length unit increases continuously more sharply as the volume flow rate increases. At the same time the scale of this increase is magnified as the diameter of the tube becomes smaller. The optimal tuning of the individual variables (volume flow rate, tube diameter, tube length, pressure drop, etc.) is performed either empirically using tests, through simulation or by means of fluidic calculations. The optimum balance is then attained when the maximum heat extraction of the heat sink is achieved with the minimum supply of energy (for a circulating pump and other units).

Furthermore, the fluidic properties of corrugated and spiral tubes are usually published by the manufacturers of such tubes (e.g. Water Way Engineering GmbH, D-47441 Moers, Germany).

FIG. 2 shows a tube 2 embodied as a corrugated tube in longitudinal cross-section, with the individual corrugations running axially symmetrically. In FIG. 3, on the other hand, a tube 2 embodied as a spiral tube is shown in longitudinal cross-section. In this case the corrugations run in a helical line around the central axis of the tube 2. 

1.-10. (canceled)
 11. A heat sink, comprising: a tube through which cooling medium can flow, wherein the tube wall of the tube is corrugated in a flow direction; and a heat-conducting material, wherein the tube is surrounded by the heat-conducting material.
 12. The heat sink as claimed in claim 11, wherein the tube is a corrugated tube with parallel corrugations.
 13. The heat sink as claimed in claim 11, wherein the tube is a spiral tube with spiral corrugations.
 14. The heat sink as claimed in claim 11, wherein the tube is manufactured from corrosion-resistant high-grade steel or copper.
 15. The heat sink as claimed in claim 11, wherein the surrounding material is selected from the group consisting of: aluminum, copper, brass, and zinc.
 16. The heat sink as claimed in claim 11, wherein the tube is formed as a tubular cavity out of the heat-conducting material.
 17. The heat sink as claimed in claim 11, wherein the heat sink has an essentially plate-shaped geometry.
 18. The heat sink as claimed in claim 11, wherein the tube is arranged in a meander shape.
 19. The heat sink as claimed in claim 11, wherein the tube is arranged in a spiral shape.
 20. The heat sink as claimed in claim 11, further comprising a water and antifreeze mixture used as the cooling medium. 